
Class OL(c- _ 



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Book 



PRESENTED BY 



LABORATORY BULLETIN NO. 13 
OBERLIN COLLEGE 



The 

Development of Nestling 

Feathers 



7 y 



BY 



Lynds Jones 



OBERLIN, OHIO 

1907 



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The Development of Nestling Feathers. 



I. INTRODUCTION. 



The purpose of this paper is to give a more complete account of the 
development of the down, or Neossoptile, than has been given by previous 
writers and to show the true relation of this structure to the first definitive 
feather. 

"The first clothing of the newly hatched bird consists of more or fewer 
soft feathers, on the whole resembling the Downs of adult birds, but possess- 
ing several characters which make it advisable to distinguish them, by the 
name of 'Neossoptiles,' from those feathers which subsequently appear, and 
may be called 'Teleoptiles,' the former being as it were the first generation 
to which others follow in constant succession, so long as the bird lives. 

"Neossoptiles are characterized by (i) a very short calamus, (2) an 
insignificant or ill-defined rachis — if there be one at all, (3) the almost 
universal absence of cilia (barbules), (4) long and slender rami (barbs), 
(5) absence of aftershaft, except in Dromaeus. To the combination of 
these characters is due the soft or downy structure of these feathers. 

"Teleoptiles, whether Contour-feathers or Downs, are each originally 
preceded by a Neossoptile, the base of which is in direct continuity with the 
tips of the rami of its succeeding final feather, but, owing to a shortened 
process of development of ccenogenetic conditions, many, or even all Neos- 
soptiles may occasionally be suppressed, so that the tips of the first feathers 
to appear are actually those of the second generation." (A Dictionary of 
Birds, A. Newton, p. 243.) 

Though a continuity between the nestling down ("Neossoptile") and 
the nestling definitive feather ( "Teleoptile" ) has been recognized, the former 
has been regarded as a relatively complete and distinct feather. I shall at- 
tempt to show that the "Neossoptile" is only a more or less differentiated 
distal part of the first "Teleoptile." 

My attention was attracted to this relationship while studying the terns 
(Sterna hirundoj S. dougalli, and S. antillarum) , and the gulls (Larus atri- 
cilld) which bred abundantly in the vicinity of Woods Holl, Mass., during 
the summer of 1903. Further study of these birds at all ages, and of nu- 
merous specimens of various species of birds, led to an examination of the 
evidence for the accepted views. 

Under the stimulus of Professor C. O. Whitman's interest and encour- 
agement the task of gathering the requisite material was carried forward. It 
would have been difficult to carry on the necessary field studies and secure 
the material from the terns and gulls but for the aid rendered by Dr. F. B. 



4 Jones — Nestling Feathers. 

Sumner, Director of the U. S. Fish Commission. To Capt. Vinal N. Ed- 
wards, of the Fish Commission, I am indebted for many valuable hints and 
advice relating to the habits of these birds; and to Dr. R. M. Strong, for 
valuable suggestions and advice. 

II. MATERIAL. 

Material for histological and cytological study was obtained from the 
following birds: Sterna hirundo, S. dougalli, Larus atricilla, and Merula 
migratoria. Developing feathers were also secured from the chick and do- 
mestic duck, incubated both artificially and naturally. Dry feathers with 
downs attached for grosser study came from the following sources : Mr. H. 
C. Oberholser, under the direction of Dr. T. S. Palmer, from the U. S. 
National Museum collections; Mr. Frank M. Chapman, from the Ameri- 
can Museum of Natural History; Messrs. C. C. Adams and N. A. Wood, 
from the collections of the University of Michigan; Prof. E. L. Moseley, 
from his private collection of American and Philippine birds ; Dr. N. Dear- 
born contributed both alcoholic and dry material from the Field Colum- 
bian Museum; and Dr. C. O. Whitman, fresh material from his pigeons. 
To all of these gentlemen I wish to express my thanks. The collections of 
Oberlin College furnished some material not obtainable elsewhere. 



III. METHODS. 



The following fixing fluids were used for chicks from five to twenty 
days' incubation: (i) Kleinenberg's picro-sulphuric mixture, (2) saturated 
aqueous solution of corrosive sublimate, (3) Hermann's fluid, (4) alcohol- 
formaldehyde mixture (70% alcohol 98 parts, 40% formaldehyde 2 parts). 
After proper fixation, pieces of skin containing the desired structures were 
cut away and later treated as ordinary histological tissues. 

For the latest stages, Hermann's fluid was found somewhat superior, 
but for the earlier stages the alcohol-formalin mixture gave the most satis- 
factory results. Since most of the material must be put into the killing and 
fixing fluids on the collecting grounds to insure a normal condition of the 
cellular structure, the latter reagent was the only one found practicable, be- 
cause the tissues could remain in it indefinitely without material injury, 
while more than five hours in the others proved fatal to good results. It 
was usually necessary to remain in the field for an entire day, because the 
nearest collecting ground was five miles away by water. Furthermore, after 
the alcohol-formalin fixation the tissues stain equally well in any of the 
stains used, even the iron hematoxylin. For the earlier stages, the Her- 
mann's fluid did not give good fixation, and it was always likely to blacken 
the tissues unequally and unduly. The picrosulphuric was very difficult to 
handle because it required a great length of time for washing out before 
stains could act ; even after two weeks of careful washing, staining was usu- 



Jones — Nestling Feathers. 5 

ally difficult and unsatisfactory. The corrosive sublimate had a strong ten- 
dency to make the tissues brittle. 

With the alcohol-formalin solution, a fixation of six hours was always 
sufficient, and four hours would often suffice. Washing out of the formal- 
dehyde was effected by the use of 70% alcohol, changing about ten times. 
Various combinations of alcohol and formaldehyde were used, but the form- 
ula given proved the most satisfactory. 

The only satisfactory method for clearing and infiltration with paraffin 
was the chloroform method. Tissues were first cleared in chloroform and 
then placed in a saturated solution of paraffin in chloroform two to five days, 
according to the thickness of the tissue. They were then transferred to 
melted paraffin for six to ten hours, and imbedded in hard paraffin (melting 
at 52 C). 

Serial sections were cut one to ten micra thick, mostly three micra. 
Complete series of all but the latest stages were easily obtained. For the 
thinnest sections, a temperature between 55 ° and 60 ° F., while cutting, was 
found necessary, and the best results were always obtained at temperatures 
not much above 60 °. 

For affixing sections to the slide a combination of the Mayer's albumen 
fixative with the water method was found the most satisfactory, but many 
times, particularly with the larger specimens, the albumen fixative was un- 
necessary. With the latest stages, where many elements were cornified, it 
was necessary to paint the dry slides, bearing sections, with a film of very 
thin celloidin solution to insure the retention of the sections during sub- 
sequent processes. These cellodin films were sometimes detached from the 
slide for quicker and more accurate staining. 

Various stains were used, the two giving the most certain and satisfac- 
tory results being Delafield's hematoxylin and the Heidenhain iron hem- 
atoxylin. Delafield's hsematoxylin was used very dilute in distilled water- — 
a pipette full of the stain to about 15OCC of distilled water, the exact pro- 
portions being unimportant. Slides left in this weak stain for 48 hours were 
always overstained, and reduction of the stain was accomplished by the use 
of weak acid alcohol. A saturated solution of eosin in 95 % alcohol was used 
in the process of dehydration for double staining, to bring out the cornifying 
elements. 

Feather germs were sectioned longitudinally, transversely and obliquely 
for all stages, and the sections were mounted in Canada balsam. A great 
deal of material was also teased on the slide and mounted in glycerine tem- 
porarily for immediate study. It was usually necessary to stain such material 
before teasing so that the structures could be seen. Dry nestling feathers 
with downy tips were dehydrated and cleared, and then mounted whole in 
Canada balsam for study of the entire feather. 

For the earlier stages of the definitive feather it was necessary to cut 
out pieces of the skin containing the desired material. All attempts to pull 



6 Jones — Nestling Feathers. 

feather germs out by means of the down were ineffectual. Likewise, barb- 
vanes pulled out were useless for any other study than that of the complete 
down, the proximal portion invariably being torn. 

Plate V represents down attached to definitive feathers photo- 
graphed enlarged. Plates VI, VII, and VIII were made by direct printing 
upon sensitive paper. In the latter case the feathers were placed upon a plate 
of clear glass, and a sheet of sensitive paper was pressed down upon them 
with the sensitive face against the feathers. The whole preparation was 
then exposed to the light in the regular printing out photographic process. 
Developing papers were used, but these gave less satisfactory results. Of 
course the prints thus obtained give very little or no color patterns. The 
feathers act as opaque objects upon the sensitive paper. This method served 
admirably where the photographic method must fail because the color con- 
trasts between the down and the definitive feather make any sort of 
a background act as a neutralizing agent for one or the other. Dividing the 
background to suit the two contrasting elements spoils the picture. 

In the further discussion of this subject it will often be necessary to 
speak of the barbs and barbules collectively, and for this purpose I shall em- 
ploy the term barb-vane. The feather-vane is made up of a median shaft 
with barbs attached on each side. The barb is the median axis of what I call 
a barb-vane, and the barbules are arranged on the barb as the barbs are sit- 
uated on the shaft. Likewise, during the earlier developmental stages of the 
down, before barb and barbule elements are clearly defined, the ridge from 
which these structures are to result will be called barb-vane ridge. 



iv. the development of the nestling down. 



A. The Feather Germ. 

Davies (1889) seems to be the last investigator to study the develop- 
mental stages of the nestling down. His is by far the most thorough and the 
most accurate treatment of the subject, but he gave no attention to the devel- 
opment of the barbs and barbules. He gave an extended review of the lit- 
erature up to the time of his work, pointing out the contribution which each 
successive author made to the subject. 

According to Davies (p. 571), the down first appears in the pigeon 
embryo on the fifth day of incubation as round white spots in the two- 
layered skin. These two layers he terms "epitrichial," outer (PI. I, Fig. 6, 
Ep) and "mucous," inner (PL I, Fig. 6, Mp). These white spots are pro- 
duced by groups of dermal cells (Drm. pp) closely pressed against the epi- 
dermis, and cause slight prominences upon the skin surface. Division of the 
mucous cells which lie over these groups of dermal cells now begins longi- 
tudinally, causing an arching of the epidermis, and the cavity in the skin 
thus formed becomes filled with dermal cells which are also rapidly dividing 
(PL I, Fig. 6). At this time the epitrichial cells undergo transverse divis- 



Jones — Nestling Feathers. 7 

ion, and this layer remains single. The dividing mucous cells, on the 
contrary, rapidly form two or more layers, or a confused mass of cells bounded 
by a well marked layer next to the derma (PL I, Fig. 7). 

In the further growth of the down papilla the cells on the anterior 
surface divide more rapidly than those on the posterior surface, so that 
the whole papilla is turned sharply backward (PL I, Fig. 1), finally 
coming to lie almost parallel to the skin surface. No sooner has this papilla 
taken a definite turn backward than cell division within it ceases except in 
a narrow region at its base just outside the skin surface; consequently all 
further growth of the papilla results from this narrow region of division and 
from the growth of the individual cells which are supplied with nutriment 
by numerous blood capillaries in the pulp. 

As long as the down papilla continues to elongate it continues to be 
an evagination of the epidermis with a core of dermal tissue. When the 
papilla has attained its full length, save for some further growth of its 
individual cells, the continued cell division results in an invagination of the 
mucous layer of the feather-germ at an angle of about 160 with the down 
papilla. At first this invagination is pushed farther in by the division of 
the cells at the skin surface, but the cell division soon changes its position 
to the proximal end of the invagination, and henceforth all growth proceeds 
from this proximal end by cell division there. This invagination is the be- 
ginning of the definitive feather (PL I, Fig. 1, grm. df). The epitrichial 
layer does not participate in this invagination, and therefore does not contrib- 
ute to the structure of the definitive feather. 

My investigations have shown that the invagination of the feather 
germ, which represents the beginning of the definitive feather, begins about 
the 1 2th day of incubation of the chick, of the duck, of the terns, and of the 
robin. My observations also indicate that with these birds differentiation of 
the definitive feather elements proceeds slowly until about the 17th day, 
after which time the definitive feathers develop rapidly. During the interval 
between the 12th and 17th days the feather rudiment seems to be engaged 
chiefly in the formation of the feather follicle. 

At the base of the down we may distinguish three sorts of cells, 
following Davies' classification. The epitrichial cells, consisting of a single 
outer layer (PL I, Fig. 6, Ep), an inner layer of mucous cells cubical in 
form and more or less regular (PL I, Fig. 6, cl. cyl), and a mass of more 
or less irregular cells between these two layers (PL I, Fig. 6, cl. im). The 
innermost layer may be distinguished as the "cylinder cell layer" (cl. cyl), 
and the irregular cells as the "intermediate cells" (cl. im). These two lay- 
ers are derived from the mucous cells by division. 

I can add little to Davies' account of the early stages in the development 
of the down. I submit Figures 1, 6, 7, 8, and 9, as amplifications of 
those given by him. His work was mostly done upon pigeon and canary 
embryos, while these figures are from a chick embryo, I have also studied 



8 Jones — Nestling Feathers. 

tern, gull, and duck embryos, all of which showed essentially the same char- 
acteristics represented by these figures. 



B. The Barbs and Barbules, 

Differentiation of the epidermal wall of the nestling down begins as 
soon as the down papilla has passed distally beyond the region of cell divis- 
ion. It therefore follows that the distal end of the down papilla is more de- 
veloped than any region proximal to it. Cross sections at different distances 
from the distal end will therefore give different stages in the development 
of the down structures. 

At the level (7, Fig. I, PI. I) where cell division has just been com- 
pleted one finds the condition represented by Figure 7, Plate I. The dermal 
nuclei are numerous and lie closely pressed against the layer of cylinder 
cells (cl. cyl), being separated from it by a basal membrane (mb. ba). A 
layer of cubical intermediate cells (cl. in) rests upon the cylinder cells, but 
peripheral to this layer the intermediate cells have become elongated and 
irregular, becoming the sheath cells (cl. tu). 

Figure 8 illustrates the condition at the level 8 in figure I, where the 
basal membrane has pushed in dividing cylinder cells and intermediate cells 
into groups. Figure 9 shows the barb-vane ridges completely separated 
from each other except at their extreme base. The cylinder cells are much 
flattened and elongated and their nuclei are far apart. The intermediate 
cells are definitely arranged into three groups — a central row of cells indi- 
cate the position of the so-called axial plate (ax. pi) and on each side of this 
plate a series of barbule cells (bbl. cl). 

It will be at once evident that the differentiation of the down barbs 
and barbules is so similar to the differentiation of the same structures 
so fully described by Strong (1902) for the definitive feather that to follow 
the steps of differentiation farther would be only to duplicate what has al- 
ready been done. Some minor differences should be mentioned. 

1. The down rudiment has a much shorter diameter and fewer ridges 
than the definitive feather. Figure 4, Plate I, represents a semidiagrammatic 
cross section at about the middle of a down from the Common Tern {Sterna 
hirundo), and Figure 5, a similar cross section of a definitive feather from 
the same species. The down has a sort of radial symmetry, the ridges being 
approximately equal in size, while the definitive feather has a decided bilat- 
eral symmetry due to the shaft rudiment X and the wedge-shaped piece 
opposite the shaft rudiment where the two vanes will separate when the 
sheath falls away. 

2. The down barbules are never provided with hooked barbicels (Fig. 
52, PI. IV), hence the down has a loose, light texture, in contrast to the firm 
texture of most definitive feathers. Although hooked barbicels are wanting 
in the down, several of the distal barbule cells send out one or two filamen- 
tous prolongations from their distal ends (Figs. 52, 55, PI. IV) which resem- 
ble the unhooked barbicels of the definitive feather barbules (Fig. 54, PL 



Jones — Nestling Feathers. 9 

IV), and are undoubtedly homologous structures. The barbules of all plumu- 
laceous feathers, and the plumulaceous proximal parts of most other definitive 
feathers lack hooked barbicels. 

3. Klee (p. 12) speaks of two chief ridges (Hauptstrahlen) in both 
the down and the definitive feather, which mark the place where the shaft 
will be developed. A few millimeters proximal to the distal end of the defin- 
itive feather such chief ridges make their appearance, but I have been unable 
to find anything corresponding to them in any down. 

4. In most descriptions of the down the statement is made that bar- 
bules are sometimes wanting upon the barbs. I have been unable to find 
any case in which this is true for the whole down except in the spike-like 
first feathers of the cuckoos. 

In the definitive feather the barb-vane ridges develop in succession 
proximally along the course of the feather, and each ridge occupies but a 
fraction of the whole length of the feather. In the down, on the con- 
trary, each barb-vane ridge is continuous through the whole length of 
the down, and usually passes without interruption into the definitive 
feather barb (PI. I, Fig. 2, PI. IV, Figs. 139, Hi, 142, Pis. V, VI, VII, 
VIII, Figs. 56 to 138). Upon this point I find myself in disagreement with 
Davies, who states (581) : "Es muss daran erinnert werden, dass die Langs- 
leisten, sobald sie sich in den Federkeimgrund erstrecken, an Umfang abneh- 
men. Die Grenze, bis zu welcher diese Verkleinerung stattfinden kann, ist 
grossem Wechsel unterworfen; jedoch in dem Falle, welchen wir als typisch 
betrachten konnen, verschwinden die Leisten vollkommen; und wenn die 
Verhornung diesen basalen Theil des Federkeimes erreicht, dann wird ein 
kurtzer horniger Cylinder gebildet, welcher mit dem Grunde der Strahlen 
in Zusammenhang steht. Dieses cylindrische Gebilde ist die sogenannte 
Spule." While Davies regarded the formation of a "quill" in the first down 
as the typical condition, he noted some variations, as further quotations will 
prove. 

"Sokh eine typische Dunenspule ist jedoch bei der Taube nicht sehr 
haufig. Gewohnlich verschwinden die Leisten nicht vollkommen, obgleich 
sie eine bedeutende Verminderung ihrer Grosse erfahren" (p. 581). 

"In der Gegend der Dunenspule nimmt der Process der Leistenbildung 
in einem grosseren oder geringeren Grad ab, oder kann sogar ganzlich auf- 
horen aber sobald wir die Spitze des definitiven Federkeims erreichen, finden 
wir ihn noch einmal in vollem Gange." 

"Zuweilen gehen die Leisten, welche oben die Dunenstrahlen hervorge- 
hen liessen, nach unten direkt in diejenigen Leisten iiber, welche die obersten 
der definitive Federstrahlen oder Aste bilden. Wenn wir bei einer in Ent- 
wicklung begriffenen Schwungfeder, welche gerade die Dune aus der Haut 
in die Hohe hebt, die Hornscheide abkratzen, welche die Wurzeln der Dun- 
enstrahlen zusammenhalt und damit den oberen Theil der definitiven Feder- 
scheide, dann sehen wir gewohnlich, dass hier und da zwei oder drei 
Dunenstrahlen an ihren Wurzeln verschmolzen sind und dass dieser versch- 
molzene theil wieder in eine grossere als die Zahl der Dunenstrahlen betragt, 




io Jones — Nestling Feathers. 

welche ihn bildeten. Auch findet man leicht einen einzelnen Dunenstrahl, 
welcher sich in zwei definitive Federaste theilt. Sogar bei vollkommener 
Verschmelzung der Dunenstrahlen und Bildung eirter typischen Spule kann 
man oft sehen, dass diese sich an ihrem tieferen Ende in vier oder fiinf 
grosse Theile auflost, welche erst allmahlich sich zertheilen, urn die definitive 
Federaste zu bilden. Wir konnen thatsachlich jeden Ubergang wahrnehmen 
zwischen der typischen cylindrischen Dunenspule und der direkten Fortset- 
zung der Dunenstrahlen in eine gleiche Anzahl von definitiven Federasten" 
(586-7). 



V. THE RELATION OF THE DOWN TO THE FIRST DEFINITIVE FEATHER. 

Klee (1886) and Davies (1889) announced that the first definitive fea- 
ther is produced by an ingrowth of the base of the down papilla, with the 
corniflcation of the proximal end of the down. In other words, the first 
down and its succeeding first definitive feather develop from the same cutis 
papilla. 

Klee (p. 39) holds that the shaft of the definitive feather is continuous 
with the shaft of the down "feather," which is clearly an error, as I shall 
show. Davies (quotation antea 7 and 8) regarded the nestling down as a 
structure typically complete in itself, possessing a quill and sometimes a shaft, 
and he considered the lack of a quill as an exceptional condition. I shall at- 
tempt to show that a shaft and a true quill are never formed, but that there 
is always a direct continuity between the barb-vanes of the down and those 
of the first definitive feather. 

There seems to be no detailed account of the manner in which the barb- 
vanes of the down pass into the barb-vanes of the first definitive feather. 
I shall therefore discuss this point at some length. 

Figures 140, 141, and 142, Plate IV, illustrate three conditions of the 
barb-vanes after complete corniflcation, in the region connecting nestling 
down with first definitive feathers. In Figure 140 the barb-vanes are united 
into a tube surrounding the pulp cavity. In Figure 141 the barb-vane has no 
connection with any other barb-vane. It divides into three definitive feather 
barb-vanes. In Figure 142 the same condition is seen, but barbules are pres- 
ent along the whole course of the barb-vane. 

Figure 140 represents the condition where a horny cylinder is formed at 
the proximal end of the down into which the down barb-vanes disappear 
proximally and out of which the definitive feather barb-vanes emerge. This 
horny cylinder is the so-called "quill" of the down. I have found this to be 
a rare condition in all birds except the Picarian and Passerine birds, where it 
is more often found than elsewhere (PI. VIII, Figs, 124 to 136, and 138). 

The condition represented by Figure 141 is a common one. Barbules 
are often lacking for a short distance — usually less than a millimeter— distal 
to the branching of the barb-vane into the definitive feather barb-vanes, when 
branching occurs; but barbules are often indicated by irregularities upon the 



Jones — Nestling Feathers. ii 

surface, or even by slight projections from the surface, representing rudimen- 
tary barbules, as in this figure. 

Figure 142 represents a common condition found among all of the water 
birds except the Anseriformes. This is undoubtedly the typical condition, as 
I hope to demonstrate in the following detailed discussion of the develop- 
mental processes which take place in the region of transition from nestling 
down into first definitive feather. 

Before discussing the development of the feather in the region which is 
supposed to lie between the down and the definitive feather, I will sketch 
in a general way the passage of a first down barb-vane into the definitive 
feather barb-vane or vanes. Figures 10 to 46, Plates II and III, have been 
prepared to illustrate the three conditions represented by Figures 140, 141, 
and 142. 

Proceeding from the down at the level 10, Figure 2, Plate I, where the 
down is complete and only waits the loss of the sheath to expand, we will fol- 
low first the process which results in the condition illustrated by Figure 141, 
Plate IV, as shown in Figures 10 to 20, Plate II. 

In Figure 10, Plate II, two down barbs are shown in cross section with 
their barbules cut at different distances from their attachment to the barbs. 
Cellular structure has been entirely obliterated by the cornification of the 
cells. Figures 10 to 20 were taken at intervals of nearly 36 microns prox- 
imally toward the distal end of the definitive feather. Barbules rapidly 
disappear and none are formed in the region of transition. The last vestige 
of a barbule will therefore be its base where it is attached to the barb. The 
medulla of the barb disappears and the shape of the barb in cross section be- 
comes somewhat circular. 

In Figure 12, remnants of nuclei begin to indicate the cellular 
origin of the barbs, and in 14 scattered cells are found in one side of 
the barb. In 15 the cells predominate, and in 16 cornification has entirely dis- 
appeared. The larger barb becomes irregular, in 17 there is an evident 
division in progress, which is completed in 18. In 19 the three cellular masses 
begin to assume the character of barb-vanes, and in 20 they are unmistakably 
barb-vanes with cylinder cells, barbule cells, and axial plate. One of the 
down barbs has remained single and has passed directly into one definitive 
feather barb, while the other has divided and merged into two definitive 
feather barbs. 

Figues 21 to 28 illustrate the passage of a down barb from a 21 -day 
chick embryo into two definitive feather barbs, after complete cornification of 
all cells. No barbules are shown. 

Figures 29 to 39, Plate III, were taken from a 21 -day chick embryo 
ready to hatch, at somewhat irregular intervals, from the region marked 29 
to 39 in Figure 3, Plate I. Figures 29 to 33 are entire cross sections of the 
down. In Figure 29 seven down barbs are seen in cross section (brb), and 
two masses of cornified material (hr) which are the fused proximal ends of 
the several remaining down barbs. Figures 30, 31, 32, and 33 illustrate the 
further fusion of the proximal ends of the barbs into cornified material (hr) 



12 Jones — Nestling Feathers. 

until all trace of individual barbs is lost (33). Passing proximally along the 
feather, Figure 34 shows this cornified material again dividing into some- 
what irregular but elongated masses. Figure 35 shows these masses becom- 
ing more regular in form and arrangement ; Figure 36 shows them assuming 
the form of a cornified barb with outlines of barbules appearing; and Fig- 
ures 37, 38, and 39 show them as definite definitive feather barb-vanes, Fig- 
ure 37 well toward complete cornification of the elements, and Figure 39 
much less cornified because this figure was taken from the pulpy tip of the 
definitive feather. It should be borne in mind that Figures 29 to 39 are 
rather oblique than exact cross sections, nearly in the line X in Figure 3, 
Plate I. All exact cross sections through the region of transition would 
show a broken cornified ring (Fig. 29, hr), because, as I have already in- 
dicated, the plane of growth is always oblique, as pointed out by Davies 
and Strong for the definitive feather. This obliquity is shown in Figure 3, 
Plate I, in the line X, which corresponds roughly to the angle which the down 
makes with the skin surface. In a plane parallel to the transverse axis of 
the down, the posterior surface is less developed. The cells here were re- 
tarded in their division while the papilla was turning backward, whereas a 
more rapid division of the cells took place on the anterior surface. 

Figures 10 to 20, Plate II, prove that at the time when the barb vane 
ridges are beginning to be differentiated as such at the distal end of the def- 
initive feather, practically all of the barb-vane elements at the proximal 
end of the down have become cornified and their cellular nature obliterated. 
Hence, in order to trace the cytology of the transition from the down barb 
into the definitive feather barb it became necessary to study feathers at differ- 
ent stages of development. We will first consider the case illustrated in 
Figure 139, Plate IV, where no barbules are formed at the extreme prox- 
imal end of the down just before it branches into definitive feather barbs. 

At X in this transition region, at an early stage in development, the 
epidermal cells are arranged as represented by Figure 7, Plate I. In other 
words, division of the mucous cells has proceeded in the usual manner — there 
is no indication that a fully formed feather will not be developed at this 
point At a little later stage of development (Fig. 40, PI. Ill) barb-vane 
ridges (brb. crs) are indicated by a more rapid proliferation of the interme- 
diate cells (cl. in) at certain places, where the cells are alike in shape and 
size, and differ from the surrounding cells. Figure 41 illustrates a still later 
stage of development, at which a group of similar intermediate cells (brb. 
crs) has become definitely separated off from those cells which surround it. 
Figure 42 shows the differentiation further progressed, Figure 43 shows the 
cornification of the cells begun and the retreat of the barb ridge toward the 
periphery, and Figure 44 cornification of the barb and almost complete oblit- 
eration of cellular structure. The whole epidermal wall is here far toward 
maturity. It is at once evident that a decreased differentiation of the inter- 
mediate cells in this region has resulted in a barb devoid of barbules. The 



Jones — Nestling Feathers. 13 

fact that relatively few of the intermediate cells are involved in the forma- 
tion of the barb indicates that the residual intermediate cells represent the 
missing barbules. 

The progress of transition which results in a so-called "quill" or tube 
differs in some important particulars from that just given. In the early 
stages of development no difference is recognizable, but at a little later stage 
the whole mass of intermediate cells (Fig. 45, PL IV, cl. in) as well as the 
sheath cells (cl. tu) become much flattened, their nuclei elongated, and their 
cell boundaries lost in a mass of fibrous tissue. Only the row of cells next 
to the pulp, representing the cylinder cell layer, retains its characteristic 
shape. At a still later stage in development, represented by Figure 46, in 
which the epitrichial sheath is not shown, cornification of the outer rows of 
cells, representing the region of the sheath cells, has taken place, only sug- 
gestions of its original fibrous structure remaining. The outermost inter- 
mediate cells have become almost wholly fibrous, narrow spaces representing 
the position of the nuclei. The process of cornification now proceeds rap- 
idly until practically all of the intermediate cells become cornifled, and the 
cylinder cell layer becomes fibrous. Figure 33, Plate III, represents the final 
stage in development. That the formation of this horny tube is wholly dif- 
ferent from the process by which the shaft and quill of the definitive feather 
are formed, as described by Davies (p. 594 et seq.), is evident. Instead 
of being a process designed for the accomplishment of a definite work — the 
building of a shaft and quill — it appears to be due to a lack of differentiation 
of the cell mass and a short cut to cornification of the tissues induced by a 
reduced blood supply to this part of the feather during the period when the 
cells would be showing differentiation if supplied with sufficient nourish- 
ment. It is significant that this condition of a cornified ring instead of the 
normal barb-vanes is more often found among the strictly altrical birds 
which are hatched in a helpless condition. It is well known that the first 
few days after the hatching of altricial birds are the most critical days of 
their lives. During this critical period there appears to be no growth of the 
down. An American robin which hatched on the fourteenth day of in- 
cubation possessed the usual down upon the head and back. These downs 
made no further growth. It was not until the fourth day after hatching 
that the skin gave evidence of the beginning of the definitive feathers. On 
the eighth day after hatching the skin surface was exposed to the drying in- 
fluences of the air before renewed activity in the feather germ began. Dur- 
ing this interval of four days the so-called "quill" was formed at the 
proximal end of the down by the rapid drying of the imperfectly formed 
barb-vane ridges. 

Although this horny cylinder seems often to be uniform in thickness for 
its whole circumference, it frequently divides along lines continuous with the 
barbs of the down, or may be made to so divide by gently rubbing it between 
two hard surfaces, thus establishing the continuity between the down barbs 
and the definitive feather barbs. 



14 Jones — Nestling Feathers. 

The material which furnished the basis for Davies' studies of the de- 
velopment of this "quill" was obtained from the canary embryo chiefly. It 
is a strictly altricial bird. 

Figure 142, Plate IV, illustrates the passage of a down barb- 
vane into three definitive feather barb-vanes where barbules are present 
along the whole course of the vane. The lengthened barbules of the down 
become shorter as the distal end of the definitive feather is approached 
and these shortened barbules gradually assume the typical character 
of pennaceous feather barbules. Figure 55 is a complete barbule taken 
at 55 in Figure 142, Plate IV, and Figure 54 is the distal four-fifths of 
another barbule taken from the region 54, Figure 142. Figure 52, Plate 
IV, represents a normal down barbule. Since barbules are present 
along the whole course of a barb of this sort there will be no interruption of 
the normal development of the barb-vane ridge, and where a down barb fs 
continuous with a single definitive feather barb, instead of with several defini- 
tive feather barbs, the only indication of the beginning of the definitive 
feather barb will be the development of hooked barbicels, provided the 
definitive feather is pennaceous in character. If the definitive feather 
is plumulaceous in character no hooked barbicels will be developed. 
It is common knowledge that the flufHness of plumulaceous feathers, like 
ostrich plumes, is due to long and slender barbules without hooks. Pen- 
naceous feathers are provided with shorter and stiffer barbules upon which 
some hooks are developed. 

The first feathers of the Anserine birds are mentioned as illustrating 
the development of both shaft and quill in the first down. My 
studies of the duck embryo prove that the first feathers begin to show as little 
papillae on the skin surface on the fifth or sixth day of incubation; that the 
insinking of the proximal end of the down begins about the twelfth 
day of incubation; and that no shaft rudiment makes its appearance until 
about the twenty-second day of incubation. New barb-vane ridges are de- 
veloped in the epidermal wall opposite to the shaft rudiment, as growth 
continues, and the ridges next to the shaft rudiment become fused into 
it laterally. The first feather continues to grow until the bird is nearly 
full grown, when a second feather begins to develop in the same papilla 
at the base of the first feather. When the second feather begins to develop 
a quill is formed at the proximal end of the first feather, but the proximal 
end of the quill has not become cornified, so that a connection is established 
between the proximal end of the quill of the first feather and the distal end 
of the second feather (Figs. 90 to 96, Plate VII). The second feather thus 
pushes the first feather out of the socket upon its tip. The connection be- 
tween the two feathers is soon broken and the first feather falls off. 

The first feather of the duck is regarded as a stiff down feather. I have 
failed to find any writer who regards it as in any sense a definitive feather, 
or a feather of the second generation. The fact that it begins to appear upon 
the skin surface on the fifth or sixth day of incubation, the time when the 
first down of other birds begins to show, indicates that there has been no short- 



Jones — Nestling Feathers. 15 

ening of feather development, and therefore proves this first feather to be the 
first down. The fact that the shaft rudiment of the first definitive feather 
of the duck does not make its appearance until after the seventeenth day of 
incubation, but that it does appear before the duckling is hatched, and that 
the first feather continues to grow for many days after the hatching, prove 
that in the development of the first feather of the duck there are stages of 
development which are exactly paralleled during the development of the 
down and first definitive feather of other birds. These stages may be briefly 
summarized for the sake of comparison. ' 

From the fifth or sixth day of incubation to about the twelfth day of 
incubation the first feather is a slender outgrowth of the epidermis with a 
dermal core. From the twelfth to the seventeenth day an invagination at 
the proximal end of the first feather occurs and a feather pocket is formed. 
On or about the eighteenth day that portion of the feather which lies within 
the skin surface begins to enlarge. About the twenty-third day the shaft 
rudiment is formed by the coalescing of two barb-vane ridges. From this 
time onward barb-vane ridges are becoming merged into the shaft rudiment 
and new barb-vane ridges are being developed in the epidermal wall of the 
feather opposite to the shaft rudiment. At the limit of growth of the feather, 
barb-vane ridges cease to develop and a quill is formed by a process fully 
described by Davies for the definitive feather (p. 597, et seq.). 

These stages of development and growth cover the whole period of the 
development and growth of the first down and the first definitive 
feather of most birds, but of only the first feather of the duck. The first 
feather of the duck is therefore a combination of the first down and 
the first definitive feather of other birds, and undoubtedly represents the 
primitive relation between these two structures. The first down is 
morphologically the distal end of the first definitive feather. This relation 
is very marked in Figure 58, Plate V, in Figures 70 and 71, Plate VI, and 
in Figures 97 and 101, Plate VII. Figure 85, Plate VI, represents a condi- 
tion found where a plumulaceous definitive feather follows a first down. 
Except for the distinct growth mark where barbules are lacking, 
there is scarcely a difference in structure between the barb-vanes of the two 
parts of this feather. In a pennaceous feather the barbs and barbules are 
shorter and stiffer. Most definitive feathers are partly pennaceous and 
partly plumulaceous, so that in a single feather are combined the rigidity of 
the pennaceous definitive feather and the soft fluffiness of down. 

Davies makes the statement that in the course of development of the 
down the pulp tissue pushes in between the barb-vane ridges and 
finally comes to surround the ridges almost completely, only a thin layer of 
cells serving to attach the ridge to the feather sheath as the peritoneum at- 
taches the digestive tube to the body wall (p. 581). Only one of his fig- 
ures (7) partially supports this statement, and it is diagrammatic. Strong 
did not find such a condition in the definitive feather, and I have failed to 
find it at any stage in the development of the first down. I have 
prepared Figures 47 to 51, Plate IV, to illustrate the conditions at the distal 



1 6 Jones — Nestling Feathers. 

end of a first down of a fourteen-day chick embryo (47 to 50 and 1, Figure 
I, Plate I). 

Figure 47 represents two barb-vane ridges in cross section distal to 
where the most distal barbules become attached to the barb. These two 
barb-vane ridges show a decided reduction in the number of barbule cells 
(bbl. cl) all of which are large. The cylinder cell layer (cl. cyl) has begun 
to separate the barb vane ridge from the sheath cells. The axial plate (ax. pi) 
is represented by large, irregular cells. There is a well developed basal 
membrane (mb. ba) which confines the dermal pulp to the center of the 
feather rudiment. In Figure 48 the barbule cells remain the same in num- 
ber, but all of them are cut nearer their distal ends, and are therefore 
smaller. The cylinder cell layer more nearly separates the barb-vane ridge 
from the sheath cells. In Figure 49 barbule cells have disappeared, but the 
barb rudiment persists as a row of cells within the complete sheath of cylin- 
der cells; in the center four cells represent the medulla of the barb. Resid- 
ual cells occur between the ridges, and a basal membrane still shuts the 
pulp away from the barb-vane ridges and the spaces between them. In 
Figure 50 nine barb-vane ridges are cut across at different distances from 
their distal ends. They are in reality rings of cylinder cells enclosing cells 
which are destined to form the extreme distal ends of the down barbs. 
Residual cells fill the spaces between the barb-vane ridges, and a basal mem- 
brane confines the dermal pulp to the central region of the feather. In 
Figure 51 the feather rudiment is reduced to the feather sheath and central 
pulp separated by a series of residual cells. Barb-vane ridges have entirely 
disappeared. 



Jones — Nestling Feathers 



Plate I 





^c&mggm?- mbM 



7 



Drrn.pp 




bbl.cl 
ax.pl 
dcyl 



grm.df 




brb.crs 




3 brb 



tu.ep 




Jones — Nestling Feathers. 



plate II. 

Figures 10 to 20 are from an 18-day chick embryo. Figures 21 to 28 are 

from a 2 1 -day embryo ready to hatch. 
Figs. 10 to 20. A series of cross sections of two barb vanes in the region 

of transition from the nestling down to the first definitive feather. At 

10 to 20. Plate I, Figure 2. x 323. 
Figs. 21 to 28. A series of cross sections of a single first down feather 

barb which was wholly cornihed, to illustrate the passage of the first 

down barb into two first definitive feather barbs, x 618. 



Jones — Nestling Feathers. 



Plate II 



tu.ep 



lu.ep 



tu.ep 




tu.ep 




Jones — Nestling Feathers. 



PLATE in. 

All figures are from a 20-day chick embryo. 

Figs. 29 to 33. Entire cross sections of down, x 141. All cellular struct- 
ure has disappeared. 

Figs. 34 to 39. Cross sections of the feather, passing proximally into the 
distal end of the definitive feather. 34, 35, and 39. x 618. 36, 37, 
and 38. x 323. 

Figures 29 to 39 form a series to illustrate the passage of the down into 
the definitive feather when a so-called "quill" is formed, that is, when 
the individual down barbs are lost in a horny ring, at Fig. 3, Plate I. 

Figs. 40 to 44. Cross sections at X in Figure 2, Plate I, at different 
stages in the development of this region, to illustrate the reduced dif- 
ferentiation of the cells which results in a barb devoid of barbules. 40, 
41, and 42. x 371. 43 and 44. x 516. 



Jones — Nestling Feathers. 17 

vi. summary. 

1. The development of the barbs and barbules is similar in the first 
down and the definitive feather. 

2. The barbule cells of the down never develop hooked barbicels, 
but some of the distal cells may give off filamentous barbicels from their 
distal end. These filamentous barbicels are homologous with the barbicels 
which are developed from the definitive feather barbule cells. 

3. The first down has no shaft. The barb-vanes which compose the 
first down are continuous and separate through the entire length of the 
down. 

4. The first down has no quill. The down barb-vanes pass without 
interruption into the first definitive feather barb-vanes, either as entirely sep- 
arate barb-vanes or else as a more or less homogeneous horny cylinder which 
can be split along lines continuous with the barb-vanes by pressing or rub- 
bing the so-called "quill" between two hard surfaces. The horny cylindri- 
cal connection between the down and the first definitive feather is frequent 
among birds whose period of incubation is less than seventeen days. 

5. No shaft is formed at the extreme distal end of the first definitive 
feather. The rudiments of a shaft begin to appear several millimeters prox- 
imal to the distal end of the feather by the coalescing of two or more barb- 
vane ridges. 

6. The dermal pulp tissue is confined to the central region of the 
first down and does not separate the barb-vane ridges from each other nor 
from the layer of sheath cells at any stage of development. This is also true 
of the definitive feather. 

7. The first down and its succceeding definitive feather are pro- 
duced by one continuous growth, and therefore cannot be regarded as two 
distinct feathers. The first down is the plumulaceous tip of the first defini- 
tive feather. 

8. Barbules are rarely entirely lacking in the first down. A typical 
down barbule is made up of a number of lengthened barbule cells placed 
end to end, the resulting barbule being long and slender, and not differing 
from the barbules of plumulaceous definitive feathers. 



1 8 Jones — Nestling Feathers. 

vii. bibliography. 

Chapman, Frank M. 

1905. A Contribution to the Life History of the American Flamingo 
( Phcenicopterus ruber), with Remarks upon Specimens. Bull. Am. 
Mus. Nat. Hist. Vol. XXI, Art. VII, pp. 53-77- 
Davies, H. R. 

1889. Die Entwicklung der Feder und ihre Beziehungen zu anderen 
Integumentgebilden. Morph. Jahrb., Bd. 15, pp. 560-645, Taf. 
23-26. 
Klee, R. 

1886. Bau und Entwicklung der Feder. Hallersche Zeitschr. f. Na- 
turwiss Bd. 59, Heft 2, pp. 1 10-156, Taf. 18-20. 
Lwoff, W. 

1884. Beitrag zur Histologic des Haares, der Borste, des Stachels, 
und der Feder. Bull. Soc. imp. Moscou, Tome 59, Pt. 1, pp. 141- 
174, Taf. 5-8. 
Studer, T. 

1873. Die Entwicklung der Feder. Inaug-Dissert. (Philos.) Facult. 
Bern. 29 p., 2 Taf. 
Studer, T. 

1878. Beitrag zur Entwicklungsgeschichte der Feder. Zweitschr. f. 
wiss. Zool., Bd. 30, pp. 421-436, Taf. 25, 26. 
Strong, R. M. 

1902. The Development of Color in the Definitive Feather. Bull, of 
the Mus. of Comp. Zool., Harvard Coll., Vol. XL, No. 3, pp. 147- 
185, PL 1-9- 



EXPLANATION OF ABBREVIATIONS. 

ax. pi. Axial plate. Drm. pp. Derma of papilla. 

bbl. Barbule. dst. Distal. 

bbl. cl. Barbule cell. Ep. Epitrichial layer. 

brb. Barb. fiL Barbule cell filament. 

brb'. Down barb. grm. df. Definitive feather germ. 

brb. crs. Barb ridge or vane. hr. Cornified tissue. 

brb. df. Definitive feather barb. mb. ba. Basement membrane. 

cl. cyl. Cylinder cell layer. med. Medulla. 

cl. im. Mucous intermediate cell Mp. Malpighian layer. 

layer. nl. Nucleus. 

cl. in. Intermediate cell. nil. Nucleolus, 

cl. pig. Pigment cell. pip. Down pulp, 

cl. tu. Sheath cell layer. pp'. Down papilla, 

cpl. sug. Red blood corpuscle. prx. Proximal, 

ctx. Cortex. tu. ep. Epitrichial sheath, 
drm'. Derma. 



Jones — Nestling Feathers. 



plate I. 

Figures I, 6, 7, 8, 9, from the chick embryo. Figures 4 and 5, from 
embryo of Sterna hirundo. Figures 2 and 3, semidiagrammatic from feathers 
of Larus atricilla. 
Fig. 1. Longitudinal section of developing down and cross section of skin 

from 14-day embryo, x 28. 
Fig. 2. Diagram showing the relation of the down to the first definitive 

feather when each down barb is continuous with one or more first defin- 
itive feather barbs. 
Fig. 3. Diagram showing the relation of the down to the first definitive 

feather when a so-called quill occurs between them. 
Fig. 4. Semidiagrammatic cross section of down, x 141. 
Fig. 5. Semidiagrammatic cross section of a definitive feather, x 103. 
Fig. 6. Portion of a down papilla from 8-day embryo, longitudinal section 

of the papilla, x 618. 
Fig. 7. A portion of a cross section of down at 7 in Figure 1. x 618. 
Fig. 8. A portion of a cross section of down at 8 in Figure I. x 618. 
Fig. 9. A portion of a cross section of down at 9 in Figure 1. x 618. 

Figures 7, 8, and 9 represent three stages in the development of the 
down at the time when the insinking of the base begins. 



Jones — Nestling Feathers. 



Plate TIT 




Jones — Nestling Feathers. 



PLATE IV. 

Figs. 45 and 46. From a 20-day chick embryo, x 618. Taken in the re- 
gion marked X, Figure 3, Plate I, at different stages in the development 
of this region. 

Figs. 47, 48, 49. Cross sections of barb-vane ridges at 47, 48, 49, Figure 1, 
Plate I. x 618. 

Figs. 50 and 51. Entire cross sections at 50 and 1, Figure 1, Plate I. 
x 618. 

Fig. 52. A completely cornified down barbule from Larus atricilla. x 330. 

Fig. 53. Distal ^5 of a down barb with barbules, from Larus atricilla. 
X28. 

Fig. 54. A barbule with filaments (fil), one of which is a hooklet or ha- 
mule, at 54, Figure 142. 

Fig. 55. A barbule with filaments (fil) at 55, Figure 142. 

Fig. 139. A down barb dividing into two definitive feather barbs, one de- 
finitive feather barb having broken away. From a fully fledged Crym- 
ophilus fulicarius. x 62. 

Fig. 140. Four down barbs passing into definitive feather barbs, showing 
incomplete separation of the barbs. From a fully fledged Oxyechus 
vocifera. x 28. 

Fig. 141. A single down barb passing into three definitive feather barbs. 
From a fully fledged Actitis macularia. x 28. 

Fig. 142. A single down barb dividing into three definitive feather barbs. 
Barbules are fully developed along the whole course of this feather. 
From a fully fledged juvenile Larus atricilla. x 39. 



Jones — Nestling Feathers. 



Plate IV 




Jones — Nestling Feathers. 



plate v. 

All figures are photographs of definitive feathers with down attached. 
xiy 2 . 
Figs. 56 and 57. American Woodcock (Philohela minor). 
Fig. 58. Killdeer (Oxyechus vocifera). 
Figs. 59, 60, and 61. Spotted Sandpiper {Actitis macularia). 
Fig. 62. Laughing Gull (Larus atricilla). 
Fig. 63. American Osprey (Pandion haliatus carolinensis) . 
Fig. 64. Red-billed Tropic Bird (Phathon athereus). 
Figs. 65 and 66. Cormorant sp? (Phalacrocorax spf). 
Figs. 67 and 68. Bob-white {Colinus virginianus) . 
Fig. 69. Chick (Gallus). 



Jones — Nestling Feathers. 



Plate V 





Jones — Nestling Feathers. 



plate VI. 

All figures are direct prints of definitive feathers with down attached, x I. 

Fig. 70. Holboell Grebe (Colymbus holboellii). 

Fig. 7 1 * Least Grebe {Colymbus dominicus brachypterus). 

Fig. 72. Pied-billed Grebe (Podilymbus podiceps). 

Fig. 73. Loon (Gavia imber). 

Fig. 74. Whiskered Auklet (Simorhynchus pygmaa). 

Fig. 75. Dovekie (A lie die). 

Fig. 76. Herring Gull (Larus argentatus). 

Fig. 77. Laughing Gull (Larus atricilla). 

Fig. 78. Common Tern (Sterna hirundo). 

Fig. 79. Roseate Tern (Sterna dougalli). 

Fig. 80. Least Tern (Sterna antillarum) . 

Fig. 81. Black Tern (Hydrochelidon nigra surinamensis) . 

Fig. 82. Sooty Tern (Sterna fuliginosa). 

Fig. 83. Anhinga (Anhinga anhinga). 

Fig. 84. Man-o'-War Bird (Fregata aquila). 

Fig. 85. Audubon Shearwater (Puffinus auduboni). 

Fig. 86. Booby sp? (Sula spf). 

Fig. 87. Red-billed Tropic Bird (Phaethon cetherus). 

Fig. 88. Leach Petrel (Oceonodromas leucorhoa) 

Fig. 89. Blue-faced Booby (Sula nebauxii). 



Jones — Nestling Feathers. 



Plate VI 





Jones — Nestling Feathers. 



plate VII. 

All figures are from direct prints of definitve feathers with down attached 

to their tips, x I. 
Figs. 90 and 91. American Merganser (Merganser americanus) . 

Ruddy Duck (Erismatura jamaicensis). 

Mexican Duck (Anas diazi). 

Pintail (Dafila acuta). 

American Golden-eye (Clangula clangula americana). 

Canada Goose (Branta canadensis). 

American Flamingo (Phanicopterus ruber). 

White Ibis (Guara alba). 

American Bittern (Botaurus lentiginosus). 

Florida Gallinule (Gallinula galeata). 

Virginia Rail (Rallus virginianus) . 

American Coot (Fulica americana). 

American Avocet (Recurvirostra americana). 

Red Phalarope (Crymophilus fulicarius). 

Northern Phalarope (Phalaropus lobatus). 

American Woodcock (Philohela minor). 

Wilson's Snipe (Gallinago delicata). 

Pribilof Sandpiper (Arquatella ptilocnemis). 

Western Solitary Sandpiper (Helodromas solitarius cinnamo- 
meus). 

Yellow-legs (Totanus flavipes). 

Western Sandpiper (Ereunetes occidental^) . 

Mountain Plover (Podasocys montanus). 

Semipalmated Plover (JEgialitis semipalmata) . 

Domestic Fowl (Gallus domesticus). 

Bob-white (Colinus virginianus). 

Red-tailed Hawk (Buteo borealis). 

American Osprey (Pandion haliatus carolinensis) . 

Barred Owl (Syrnium varium). 



Fig. 


92. 


Fig. 


93- 


Fig. 


94- 


Fig. 


95. 


Fig. 


96. 


Fig. 


97- 


Fig. 


98. 


Fig. 


99- 


Fig. ] 


[00. 


Fig. ] 


[01. 


Fig. ] 


[02. 


Fig. ] 


[03. 


Fig. ] 


[O4. 


Fig. ] 


[05- 


Fig. ] 


[06. 


Fig. ] 


[07. 


Fig. ] 


[08. 


Fig. ] 


[09. 


Fig. ] 


[10. 


Fig. ] 


[II. 


Fig. ] 


[12. 


Fig. ] 


[13. 


Fig. ] 


[14. 


Fig. ] 


[15. 


Fig. ] 


[16. 


Fig. ] 


[17. 


Fig. ] 


[18. 



Jones — Nestling Feathers. 



Plate VII 











ifw ?T 






r^| 












i * j 




E <^h 




■■ ti^H 




a A 


P^:^ft^l 


■^^^j3| ' 


F7 




V {i i'i : ' : .± 


T^V ' y 








^^H BE 


1 J 




tgrl 






iuIMBwBhII 1 


E^' 


■' v. • 












Mh£ |jflj§ 


1 102 1 


103| 




HI 1 105 1 ! 

104 1 


fclQQJ 


1 101 1 










B J 












[7 










ifl 




pn^j 


j ifi ios 


'., -C. Bio 9 




inoj wJm 

■1 ■ ■ 


[ "^^P 


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BBvf<#| 


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fmj 


ii"i 


pi^ 


pVI "" 


_njj 


pRl?1 i us i 



Jones — Nestling Feathers. 



plate VIII. 

All figures are from direct prints of definitive feathers with down attached 
"r tips, x i. 
Screech Owl (Megascops asio). 
Great Horned Owl (Asio virginianus). 
Nighthawk (Chordeiles virginianus) . 
Whippoorwill {Antrostomus vociferus). 
Nuttall's Poorwill (Phalcenoptilus nuttallii). 
American Crow (Corvus brachyrhinchos) . 
Cowbird (Molothrus ater). 
Baltimore Oriole (Icterus galbula). 
Meadowlark (Sturnella magna). 
Red-winged Blackbird (Agelaius phceniceus). 
Red-eyed Vireo (Vireo olivaceus). 
Blue Jay (Cyanocitta cristata). 
Bobolink (Dolichonyx oryzivorus). 

Red-headed Woodpecker (Melanerpes erythrocephalus). 
Red-headed Blackbird (Agelaius phceniceus). 
Catbird (Galeoscoptes carolinensis). 
Song Sparrow (Melospiza cinerea melodia). 
Cowbird (Molothrus ater). 
Green Heron (Butoridcs virescens). 
American Robin (Merula migratoria) . 





o th 


Fig. 


119. 


Fig. 


120. 


Fig. 


121. 


Fig. 


122. 


Fig. 


123. 


Fig. 


124. 


Fig. 


125. 


Fig. 


126. 


Fig. 


127. 


Fig. 


128. 


Fig. 


129. 


Fig. 


130. 


Fig. 


I3i- 


Fig. 


132. 


Fig. 


133- 


Fig. 


134- 


Fig. 


135. 


Fig. 


136. 


Fig. 


137. 


Fig. 


138. 



Jones— Nestling Feathers. 



Plate VIII 




LB S '08 



' 



